Most vitamins are useless, but here are the ones you should take

It seems like simple, obvious advice: Eat your vegetables, get some exercise, and — of course — take your vitamins.

Or not.

Decades of research has failed to find any substantial evidence that vitamins and supplements do any significant good. In fact, recent studies skew in the opposite direction, having found that certain vitamins may be bad for you.

Multivitamins: Skip them — you get everything you need with a balanced diet.

For decades, it was assumed that multivitamins were critical to overall health. Vitamin C to "boost your immune system," Vitamin A to protect your vision, Vitamin B to keep you energized.

Not only do you already get these ingredients from the food you eat, but studies suggest that consuming them in excess can actually cause harm. A large 2011 study of close to 39,000 older women over 25 years found that women who took them in the long term actually had a higher overall risk of death than those who did not.

Vitamin D: Take it — It helps keep your bones strong and it's hard to get from food.

Vitamin D isn't present in most of the foods we eat, but it's a critical ingredient that keeps our bones strong by helping us absorb calcium. Getting sunlight helps our bodies produce it as well, but it can be tough to get enough in the winter. Several recent study reviews have found that people who took Vitamin D supplements daily lived longer, on average, than those who didn't.

Antioxidants: Skip them — an excess of these has been linked to an increased risk of certain cancers, and you can eat berries instead.

Vitamins A, C, and E are antioxidants found in plentiful form in many fruits — especially berries — and veggies, and they've been touted for their alleged ability to protect against cancer.

But studies suggest that when taken in excess, antioxidants can actually be harmful. A large, long-term study of male smokers found that those who regularly took Vitamin A were more likely to get lung cancer than those who didn't. And a 2007 review of trials of several different types of antioxidant supplements put it this way: "Treatment with beta carotene, vitamin A, and vitamin E may increase mortality."

Vitamin C: Skip it — it probably won't help you get over your cold, and you can eat citrus fruits instead.

Vitamin B3: Skip it and eat salmon, tuna, or beets instead.

For years, Vitamin B3 was promoted to treat everything from Alzheimer's to heart disease. But recent studies have called for an end to the over-prescription of the nutrient.

A large 2014 study of more than 25,000 people with heart disease found that putting people on long-acting doses of Vitamin B3 to raise their levels of "good," or HDL, cholesterol didn't reduce the incidence of heart attacks, strokes, or deaths.

Plus, people in the study who took the B3 supplements were more likely than those taking a placebo to develop infections, liver problems, and internal bleeding.

Probiotics: Skip them — the science isn't advanced enough yet for them to have a significant benefit, and you can eat yogurt instead.

Probiotics — pricey bacterial supplements that can cost upward of $1 per pill but are found naturally in smaller amounts in yogurt and other fermented foods — have become a big business with a market of roughly $23.1 billion in 2012.

The idea behind them is simple: Support the trillions of bacteria blossoming in our gut which we know play a crucial role in regulating our health.

But putting that idea into actual practice has been a bit more complicated. So far, the effects of probiotics have been all over the map. Sometimes they help, sometimes they don't. So rather than shelling out for a pill that promises to be a cure-all, snack on a parfait.

Zinc: Take it — it's one of the only ingredients linked to shortening a cold.

Unlike Vitamin C, which studies have found likely does nothing to prevent or treat the common cold, zinc may actually be worth it. The mineral seems to interfere with the replication of rhinoviruses, the bugs that cause the common cold.

In a 2011 review of studies of people who'd recently gotten sick, researchers looked at those who'd started taking zinc and compared them with those who just took a placebo. The ones on the zinc had shorter colds and less severe symptoms.

Vitamin E: Skip it — an excess has been linked to an increased risk of certain cancers, and you can eat spinach instead.

The antioxidant Vitamin E was popularized for its alleged ability to protect against cancer. But a large 2011 study of close to 36,000 men found that the risk of prostate cancer actually increased among the men taking Vitamin E compared to the men taking a placebo.

And a 2005 study linked high doses of Vitamin E with an overall higher risk of death. So if you're looking for more Vitamin E, make yourself a fresh spinach salad and skip the pill. Dark greens like spinach are rich with this stuff.

Folic acid: Take it if you're pregnant or if you might want to get pregnant.

Folic acid is a B vitamin which our bodies use to make new cells. The National Institutes of Health recommends that women who are currently pregnant or who want to get pregnant take 400 micrograms of folic acid daily because their bodies demand more of this key nutrient when they are carrying a growing fetus.

Additionally, severallargestudies have linked folic acid supplementation before and during pregnancy with decreased rates of neural-tube defects, serious and life-threatening birth defects of the baby's brain, spine, or spinal cord.